Magnetic separation of particular mixtures

ABSTRACT

Particulate mixtures of non-magnetic or paramagnetic materials are separated by selectively coating the surfaces of a component or components of the mixture with a magnetic fluid. Thereafter, the particulate mixture is subjected to a magnetic separation yielding a magnetic fluid-coated fraction and a non-magnetic fraction. The process is especially useful in mineral beneficiation wherein a mineral concentrate is recovered from its ore.

United States Patent 1191 Shubert 1 MAGNETIC SEPARATION OF PARTICULARMIXTURES [75] Inventor: Roland H. Shubert, Reston, Va.

[73] Assignee: Maryland Patent Development Co.,

Inc., Silver Spring, Md.

[22] Filed: July 5, 1973 [21] Appl. No.: 376,335

[52] US. Cl. 209/8; 209/49; 209/214 [51] Int. Cl. B030 1/00 [58] Fieldof Search 209/8, 8.1, 9, 49, 214,

[ Dec. 16, 1975 1,043,850 11/1912 Lockwood 209/8 X 1,043,851 11/1912Lockwood 209/8 1,823,852 9/1931 Brandus 209/9 X 3,214,378 10/1965Mannemon 252/6252 3,272,758 9/1960 De Lew 210/42 X 3,635,819 1/1972Kaiser 210/40 Primary Examiner-Robert l-lalper 57 ABSTRACT Particulatemixtures of non-magnetic or paramagnetic materials are separated byselectively coating the surfaces of a component or components of themixture with a magnetic fluid. Thereafter, the particulate mixture issubjected to a magnetic separation yielding a magnetic fluid-coatedfraction and a non-magnetic fraction. The process is especially usefulin mineral [56] References Cited I UNITED STATES PATENTS beneficlatlonwherein a mineral concentrate is recovered from its ore.

933,717 9/1909 Lockwood 209/8 959,239 5/1910 Lockwood 209/8 26 Claims, 2Drawing Figures 990,491 6/1911 Lockwood 209/8 MAGNETIC PARTICULATE FLUIDMIXTURE IO Mu s CONTACT SEPARATE 18 l 1 E n lme- U.S. Patent Dec. 16,1975 3,926,789

MAGNETIC PARTICULATE FLUID MIXTURE EMULSIFY CONTACT SEPARATE l8 L 1 n heORE coumnonme il 1 AGENT 4| GRIND CONDITION CONTACT L SEPARATE i I Q E.

GANGUE43 57 |---'-L.--1 MAGNETIC 1 DRY MINERAL FLUID 46 L... 1.

EMULSIFY Ra a a9 4 8 MINERAL ----1--- 49 WATER 50w GANGUE FIG. 2

MAGNETIC SEPARATION OF PARTICULAR MIXTURES I BACKGROUND or THE INVENTIONMagnetic separation of particulate mixtures is highly developed andlong-practiced. The technique may be practiced as a wet process, such asin a water slurry, or may be used to separate a dry particulate mixture.

Magnetic separation is cheap, highly selective, efficient and lendsitself to both small scale and large volume uses. It is fundamental, ofcourse, that a practical magnetic separation process requires either thedesired or the reject fraction of the mixture treated be magnetic. Sincethe vast majority of particulate mixture separated on an industrialscale comprise materials which are diamagnetic, or at best paramagnetic,magnetic separation has remained a special purpose type of processsuited only to a relatively few uses.

Efforts have been made in the past to alter the properties of materials,especially minerals, to render them magnetic. It is known, for examplethat the magnetic properties of many minerals can be altered bysubjecting them to a heat treatment. This is the simplest and at thistime probably the only practical method for altering magnetic propertiesof most materials. The process may be accomplished by a simple heatingas in the case of pyrite which loses sulfur and is converted topyrrhotite at temperatures on the order of 600C: an oxidizing roast asfor many sulfides: a reducing roast as for hematite and other ironoxides or may be a combination of these and similar treatment steps.Examples of minerals which are known to display increased magneticactivity after heat treatment include pyrite, hematite, marcasite,siderite, chalcopyrite, arsenopyrite, bomite and pyrolusite.Temperatures required in the heat treatment step generally range fromabout 300 to 1000C. While heat treatment to enhance the magneticproperties of such minerals is technically feasible, it is seldomeconomically practical. Copper sulfide ores, such as bornite andchalcopyrite for example, seldom exceed a few percent copperconcentration. A heat treatment of such an ore to render the coppersulfide magnetic preparatory to a magnetic separation would require theheating of vast qualities of gangue which makes the techniqueeconomically prohibitive. Attempts have also been made to cause amagnetic particle to attach to a non-magnetic particle and thus allow amagnetic separation to be performed with recovery of the non magneticparticle. A description of some such attempts and a discussion of theirrelative successes and limitations are set out in the l-Ierkenhoffpatent, US. Pat. No. 2,423,314 and in the Gompper patent, US. Pat. No.2,828,010.

SUMMARY OF THE INVENTION I have found that particulate mixtures ofnon-magnetic or paramagnetic materials may be separated by selectivelyrendering magnetic the surfaces of one or more components contained inthe mixture and thereafter subjecting the mixture to a magneticseparation. Surfaces of selected components contained in the mixture aremagnetized by selectively coating these components with a magneticfluid.

The selective coating step is preferably accomplished with theparticulate mixture in liquid suspension. Thereafter, the magneticseparation may be accomplished either directly from the liquidsuspension or the 2 particulate mixture may be separated from liquidsuspension dried and subjected to a dry magnetic separation. My processis particularly applicable to the beneficiation of minerals; especiallyto the separation, concentration and recovery of metal values from theirnaturally occuring ores.

Hence, it is an object of my invention to selectively magnetize at leastone component of a particulate mixture.

It is another object of my invention to separate particulate mixtures ofnon-magnetic and paramagnetic materials by magnetic means.

Another object is to separate minerals from their associated gangue.

One specific object of my invention is to separate and recover metalvalues from their naturally occuring ores.

Yet another specific object of my invention is to recover coal from coalwastes.

DETAILED DESCRIPTION OF THE INVENTION In the drawings,

FIG. 1 is a diagrammatic flow sheet depicting a general embodiment of myprocess.

FIG. 2 depicts a specific embodiment of my process directed to therecovery of a mineral concentrate from its ore. Both Figures will bediscussed in detail later.

I have found that a film of magnetic fluid may be selectively applied toone or more components of a particulate mixture and that the appliedmagnetic film renders those components sufficiently magnetic as to allowa simple magnetic separation to be performed upon the mixture. Myprocess is especially applicable to relatively finely dividedparticulate mixtures such as those normally encountered in thebenefication of ores.

Magnetic fluids useful in my process include those fluids which havebecome known in the art as ferrofluids. Magnetic fluids, or ferrofluids,are ultra-stable colloidal suspensions of magnetic particles in a liquidcarrier. These fluids behave as homogenious Newtonian liquids and canreact with an external magnetic field. The liquid carrier or base may bea hydrocarbon, fluorocarbon, silicone oil, water, ester or similarliquid. Magnetic fluids are commercially available in a range of liquidcarriers and display a saturation magnetization as high as about 1000gauss. Such fluids may be produced by several different methods.Magnetic fluids were first produced by the long term grinding ofmagnetite in a hydrocarbon such as kerosene containing an appropriatedispersing agent such as oleic acid. This technique is set out in thePapell patent, US. Pat. No. 3,215,572. Magnetic fluids may also beproduced by the method of Reimers and Khalafalla which is described inU.S. patent application Ser. No. 275,382; now US. Pat. No. 3,843,540. Anexcellent review of the properties and behavior of magnetic fluids maybe found in an article by R. E. Rosensweig entitled Magnetic Fluids andappearing in International Science & Technology, July, 1966, pp. 4856.

My invention resides in the discovery that magnetic fluids can be causedto selectively wet and coat particles of one composition in admixturewith particles of differing composition. The coating so formed isadherent and of sufficient magnetic strength as to render the coatedparticle responsive to a magnetic field. Hence the coated particles maythereafter be separated from non-coated particles by conventionalmagnetic separation techniques.

In principle, the reason that magnetic fluids can be caused toselectively coat particles of one composition while leaving otheradmixed particles unaffected depends upon the relative wettability ofthe particle surfaces. Desired selectivity may be influenced in a numberof different ways. One method for achieving selectivity is by choice ofthe liquid carrier making up the magnetic fluid. For example, mostminerals exhibit a strongly polar surface and thus are wetted by waterbut not by hydrocarbon. Hence, a hydrocarbon base magnetic fluid willnot wet such minerals. However, some minerals tend to exhibithydrophobic surfaces and a hydrocarbon base magnetic fluid will readilywet those while leaving particles having a polar surface unaffected.Examples of such minerals include a variety of carbonaceous metal ores,anthracite and other coals and some metal sulfides such as molybdenite.Thus, a mixture containing particles displaying both hydrophobic andhydrophilic surface properties may be directly treated with ahydrocarbon base magnetic fluid resulting in the selective coating ofthe hydrophobic particle surfaces with the magnetic fluid. A magneticseparation may then be performed to recover two fractions; one fractionbeing magnetic and comprising those minerals having hydrophobic surfaceproperties and the other fraction being non-magnetic and comprisingthose minerals' having hydrophilic or polar surface properties.

Proper choice of the magnetic fluid liquid carrier allows the separationof a variety of particulate mixtures. But greatly enhanced selectivityand variety of particulate mixtures amenable to separation by my processcan be achieved by modifying the surface properties of one or more ofthe components contained in the particulate mixture. Modification ofparticle surface properties may be accomplished in a fashion similar tothat used in conventional flotation processes. Flotation is a method ofmaterials separation which is based on the affinity of properly preparedmineral surfaces for air bubbles. In froth flotation, the most commonform, a froth is formed by introducing air into a suspension or pulp offinely divided particles in water containing a frothing agent. Thoseparticles having an affinity for air bubbles rise to the surface of thefroth while particles completely wetted by water remain in suspension.

Selectivity of conventional flotation processes is achieved principallyby imparting an aerophilic, or

air-avid, coating on certain classes of mineral particles,

by reactingv the mineral surfaces with Xanthates, aliphatic acids,amines and a variety of other chemicals to give in effect a hydrophobicbut aerophilic surface. In nearly all cases such an aerophilic surfaceis also organophilic and so will be readily wet by a hydrocarbon. Thisfortunate circumstance allows me to take advantage of the developedmethods of surface treating mineral particles and extends the usefulnessof my process to substantially all of the separations now accomplishedby flotation. In addition, such surface treating techniques allows theuse of hydrocarbon base magnetic fluid for most separations. This isadvantageous in that hydrocarbon base magnetic fluids are presently thecheapest and most readily available type.

In its broadest form my invention comprises contacting a particulatemixture of solid materials with a magnetic fluid. To attain a selectivecoating of magnetic fluid on one or more components of the mixture whileleaving other components substantially unaffected, it is necessary thatthe surfaces of those components to be '4 coated be readily wettable bythe magnetic fluid while the surfaces of other components must either bedifficulty wettable or non-wettable by the fluid. Coated particles arethen separated from non-coated particles by magnetic means.

Contacting the particulate mixture with a magnetic fluid may beaccomplished by tumbling or otherwise mixing or agitating the particleswith a relatively small quantity of magnetic fluid. Only enough magneticfluid need be used to form a relatively thin film upon the surfaces ofthose particles which are wet by the fluid. An excess of magnetic fluidin some cases can lead to a lessened selectivity.

In most instances, however, it is advantageous and preferred to contacta liquid suspension or pulp of the particulate mixture with magneticfluid rather than performing the contacting step in the dry state. Thisis especially true of most mineral beneficiation processes wherein it isdesired to obtain a mineral concentrate from its ore. It is conventionalpractice in most ore beneficiation processes to grind the crude ore withwater in rod or ball mills to a size range whereat there is obtainedsubstantially complete liberation of the desired mineral particles fromthe associated gangue. The slurry or pulp of ground ore is thenconditioned, usually by chemical treatment, to modify the surfaceproperties of one or more components or classes of components containedin the ore. After conditioning, the slurry or pulp is conventionallytreated by froth flotation to recover a mineral concentrate.

My process can conveniently encompass the grinding and conditioningsteps of a typical flotation process. After conditioning, if that stepis necessary or appropriate, I contact the slurry or pulp with amagnetic fluid. Contacting is best accomplished under conditions ofthorough agitation so as to uniformly disperse and coat the wettableparticles with magnetic fluid. It is advantageous, especially when usinga hydrocarbon base magnetic fluid, to first emulsify the magnetic fluidin a relatively small volume of water and add the emulsion to the pulpor slurry. Such an emulsifying step tends to reduce the amount ofmagnetic fluid needed and tends to give a more uniform coating onwettable particles than does adding the fluid directly to the aqueouspulp. Emulsification is easily accomplished by intense agitation ofwater and the magnetic fluid to form an emulsion with water as thecontinuous phase.

The minimum amount of magnetic fluid required is that sufficient to forma thin coating on the surfaces of those particles wettable by the fluid.When using my process in ore benefication, it is usually desirable toselect a fluid and appropriately condition the ore so that the mineralrather than the gangue is wet by the magnetic fluid since gangue usuallymakes up the bulk of an ore. Since particle surfaces are coated andsurface area is a function of particle size, generally the finer theparticle size the more magnetic fluid is required. Thickness of themagnetic film, and hence intensity of magnetic response, can becontrolled to some degree by the amount of magnetic fluid used. However,use of excessive amounts of magnetic fluid results in at least a portionof the excess remaining in emulsified form in the water. Further, theintensity of magnetic response of a coated particle can better becontrolledby proper choice of the saturation magnetization of themagnetic fluid used. It is also apparent that the amount of magneticfluid required is dependent upon the concentration of the magneticfluid-wettable particles in the mixture. In more specific terms, amountof magnetic fluid required to treat a particular ore appears to becomparable to the amount of flotation/reagent required for that sameore. For most ores, this will usually be in the range of about 0.01 topounds of magnetic fluid per ton of ore.

After selectively coating one component, or class of components, in theore I subject the treated material to a magnetic separation. This may beeither a wet magnetic separation in which a magnetic fraction isrecovered directly from the slurry or pulp or a dry magnetic separationmay be performed after de-watering and drying. Both techniques are wellknown and highly developed. A variety of both wet and dry magneticseparators appropriate for use in my process are commercially available.

Size range of particulate mixtures amenable to treatment by my processencompasses that range normally treated by flotation techniques.Generally the maximum diameter of mineral particles recoverable by frothflotation is on the order of 300 microns or about 50 mesh. My process isnot so limited and can be successfully used to separate particulatemixtures of much larger particle size especially if a dry magneticseparation is performed. Presence of very fine colloidal particles orslimes is undesirable in my process as it is in flotation. But myprocess appears to be less hindered by very fine particles than isflotation because the small, magnetic fluid-coated particles tend toagglomerate in the form of chains and rings.

Referring now to the drawings, FIG. 1 is a diagrammatic representationof my process applicable to particulate mixtures generally. A magneticfluid 10 and a second liquid 11 are emulsified in means 12 and theemulsion 13 is passed to contacting means 14 into which a particulatemixture 15 is introduced. Intimate mixing of the mixture 15 and emulsion13 results in the selective coating of a component or class ofcomponents of mixture 15. The treated mixture, now having selectedparticles carrying a thin coating of magnetic fluid, is passed viatransport means 16 to magnetic separator 17 which separates theparticulates into a magnetic fraction 18 and a non-magnetic fraction 19.

It is necessary that magnetic fluid 10 and liquid 11 be immiscible onein the other. Perhaps the most common example of such a system is ahydrocarbon base magnetic fluid and water. In addition, it is necessarythat the magnetic fluid selectively wet particular components of mixture15 and it is much preferred that liquid 11 selectively wet othercomponents of the particulate mixture. Particulate mixture 15 may beintroduced into contacting means 14 in a dry or semi-dry state or may beintroduced as a suspension or pulp in a liquid. If mixture 15 isintroduced as a liquid suspension, it is much preferred that the liquidbe the same as liquid 11 or completely miscible with it. As has been setout previously, it is not necessary but is preferred to emulsifymagnetic fluid 10 before it is introduced into contacting means 14.

Referring now to FIG. 2, there is shown an embodiment of my processdirected to the recovery of a mineral concentrate from its ore. An ore30 is comminuted in grinding means 31 to a size range whereat theparticles of the desired mineral are substantially physically freed fromthe matrix or gangue. The comminuted ore is sized if necessary and ispassed via means 32 to conditioning means 33 wherein the ore is treatedwith conditioning agent 34 to modify the surface properties of one ormore components of the ore. It is to be noted that this conditioningstep, though often required and generally desirable, is not necessarywith all ores. Grinding and conditioning are usually carried out usingwater as a carrier liquid. The water suspension of the ore, or pulp, istransported via means 35 to contacting means 36 werein it is intimatelymixed or contacted with an emulsion of magnetic fluid in waterintroduced via means 37. This emulsion is produced by introducing amagnetic fluid 38, preferably a hydrocarbon base magnetic fluid, and awater stream 39 into emulsifying means 40. As has been noted previously,magnetic fluid 38 may be added directly to contacting means 36 withoutbeing emulsified beforehand.

Intimate contacting of ore pulp 35 and magnetic fluid emulsion 37 inmeans 36 results in the selective coating of magnetic fluid 38 on thesurfaces the mineral particles contained in admixture with gangueparticles. The treated pulp is passed from contacting means 36 viaconduct means 41 to wet magnetic separator 42 wherein the pulp isseparated into a magnetic mineral concentrate 43 and a gangue fraction44. Alternatively, treated pulp from contacting means 36 may betransferred via means 45 to dewatering and drying means 46. After dryingto a free-flowing state, the treated ore is then transported via means47 to dry magnetic separation means 48 from which is recovered a mineralconcentrate 49 and a gangue fraction 50.

The process as embodied in FIG. 2 is applicable to a wide range of ores.Copper sulfide ores such as chalcocite, bornite and the like are oftenfound in a calcareous or siliceous matrix and typically have a coppercontent on the order of 1%. When treating an ore of this type by theprocess embodied in FIG. 2, conditioning agent 34 may be ferric chlorideand magnetic fluid 38 is preferably of hydrocarbon base. When the ore iszinc sulfide (sphalerite) then conditioning agent 34 may comprisesulfurous acid and again the preferred magnetic fluid is hydrocarbonbase. If the ore is carbonaceous, or is anthracite coal for example, theconditioning step 33 may be dispensed with entirely.

Another ore amenable to treatment by the process depicted by FIG. 2 isnon-magnetic taconite. Taconite is an iron ore comprising various oxidesof iron in a siliceous matrix. Magnetic taconites, comprising mainlymagnetite, are readily concentrated by' magnetic means. Non-magnetictaconites comprise various non-magnetic iron oxides including hematiteand present a much more formidable beneficiation problem. When treatingsuch an ore by my process, conditioning agent 34 may comprise forexample a fatty acid or sulfonic acid and, after contacting theconditioned ore with a magnetic fluid in means 36, the non-magnetictaconite may be treated in the same fashion now used to concentratemagnetic taconite.

The following specific examples will serve to further illustratespecific embodiments of my process.

EXAMPLE 1 A sample of copper ore from Tyrone, New Mexico was ground to asize range finer than about mesh. This ore is representative of thatpresently being mined at Tyrone and comprises chalcocite in a siliceousmatrix. The ground ore was slurried in water and then treated with adilute solution of ferric chloride for about 30 minutes to activate thesurface of the copper sulfide particles. The ferric chloride solutionwas then decanted off, the ore washed with water, and re-slurred in asecond measure of water. A small quantity of kerosene base magneticfluid was then added with agitation. After about 1 minute of intenseagitation, the slurry was transferred to a non-magnetic vessel.Chalcocite particles could be readily removed from the slurry using asmall hand magnet. A portion of the treated ore was then de-watered anddried. Chalcocite particles in the dried ore responded to a magnet.Gangue particles did not.

EXAMPLE 2 A sample of sphalerite (zinc sulfide) ore was ground to a sizerange finer than about 100 mesh. The ground ore was wet with water andtreated with dilute (7%) sulfurous acid for about minutes to activateand condition the surface of the sphalerite particles. After decantingthe acid from the ore, it was washed in water, re-slurred in a secondmeasure of water, and treated with a small quantity of hydrocarbon basemagnetic fluid with intense agitation. After agitation, sphaleriteparticles were magnetically responsive both in the slurry and afterdrying. Gangue particles were not.

EXAMPLE 3 The sphalerite ore of Example 2 was ground to a nominal sizerange of about 60 mesh. It was conditioned with sulfurous acid in amanner similar to that of Example 2. A quantity of kerosene basemagnetic fluid was added to water and subjected to intense agitation toform a semi-stable emulsion. The conditioned sphalerite ore was thenadded to the magnetic fluid emulsion and agitated for about 2 minutesand then transferred to a non-magnetic container. Sphalerite particlescould readily be extracted from the slurry using a small hand magnet.

Microscopic examination of the thus-extracted sphalerite particlesshowed some agglomeration into chainlike structures and ring-likestructures. The ring structures were typically made up of a single rowof sphalerite particles arranged in a ring configuration having adiameter as large as about 10 average particle diameters. This ore had acalcite matrix or gangue. A few scattered calcite particles were evidentmixed with the magnetically recovered sphalerite. These calciteparticles were clear and clean showing no signs of magnetic fluidcoating and, when physically separated from the sphalerite particles,displayed no magnetic response.

The ore was then separated from the liquid by filtration and was thendried. The liquid filtrate contained a substantial amount of theorginally added magnetic fluid still in emulsified form. In thisexperiment, the amount of magnetic fluid added was about 3% by weightbased on the weight of the sphalerite ore. In spite of the fact that asubstantial excess of magnetic fluid was used, there was no evidence ofmagnetic fluid coating or wetting of the calcite gangue particles.

Portions of the dried, magnetic fluid-treated ore were then subjected toa magnetic separation. An essentially complete separation between thegangue and sphalerite was achieved under the influence of a magneticfield of about 1000 gauss.

EXAMPLE 4 A quantity of finely ground bituminous coal was slurried inwater. Small quantities of hydrocarbon base magnetic fluid was addeddirectly to the slurry with agitation. Coal particles responded stronglyto a magnet. Ash particles did not.

EXAMPLE 5 Waste anthracite coal fines were slurried in water and treatedwith a hydrocarbon base magnetic fluid with agitation. Anthraciteparticles responded strongly to a magnet. Ash particles did not.

I claim:

1. A method of recovering a mineral from the gangue constituents of itsore which comprises:

comminuting the ore to a size range whereat there is achievedsubstantial physical liberation of the mineral from the gangueconstituents of the ore;

rendering the surfaces of the mineral particles magnetic by selectivelywetting the surfaces of said mineral particles with a magnetic fluid,said magnetic fluid comprising an ultra-stable colloidal suspension ofmagnetic particles in a liquid carrier, said liquid carrier beingselected from the group consisting of hydrocarbons, fluorocarbons,silicone oils, water and esters, said magnetic fluid being capable ofreacting with an external magnetic field and displaying the behavior ofa homogeneous Newtonian liquid, and

subjecting the comminuted ore to a magnetic separation whereby amagnetic concentrate comprising magnetic fluid-wetted mineral particlesis recovered.

2. The method of claim 1 wherein the surfaces of mineral particles arenot readily wet by water and wherein the surfaces of particulate gangueconstituents of the ore are readily wet by water.

3. The method of claim 2 wherein the magnetic fluid is immiscible withwater and wherein the mineral particles are selectively wetted with saidfluid by contacting a water suspension of said comminuted ore with anamount of magnetic fluid sufficient to form a thin film on the surfacesof mineral particles contained in the ore.

4. The method of claim 3 wherein the mineral is selected from the groupconsisting of metal sulfides, metal oxides and carbonaceous ores andwherein the magnetic fluid is hydrocarbon base.

5. The method of claim 5 wherein the comminuted ore is subjected to aconditioning steps comprising a chemical treatment which renders thesurfaces of mineral particles hydrophobic and organophyllic and whereinsaid magnetic separation is accomplished by subjecting the magneticfluid-treated ore to the influence of a magnetic field having a fieldstrength in excess of 1000 gauss.

6. The method of claim 1 wherein the comminuted ore is subjected to aconditioning step to modify the surface properties of at least oneconstituent of the ore prior to wetting the mineral particles with saidmagnetic fluid.

7. The method of claim 6 wherein said conditioning step comprises achemical treatment which renders the surfaces of mineral particleshydrophobic and organophylic.

8. The method of claim 7 wherein said conditioning I 10. The method ofclaim 9 wherein the magnetic fluid is hydrocarbon base and wherein themagnetic fluid is in the form of a water emulsion when it is broughtinto contact with the ore.

11. The method of claim 10 wherein the magnetic separation is a wetseparation whereby mineral particles wetted with magnetic fluid arerecovered from the water suspension.

12. The method of claim 10 wherein the ore suspension is de-watered anddried to a free-flowing state after being contacted with the magneticfluid and wherein the dried ore is subjected to a magnetic separation torecover a mineral concentrate.

13. The method of claim 10 wherein the ore is a copper ore and whereinsaid mineral comprises copper sulfide.

14. The method of claim 13 wherein said conditioning step comprisesreacting the surfaces of copper sulfide particles with ferric ion.

15. The method of claim 10 wherein the ore is a zinc ore and whereinsaid mineral comprises zinc sulfide.

16. The method of claim 15 wherein said conditioning step comprisesreacting the surfaces of zinc sulfide particles with a dilute acid.

17. The method of claim 10 wherein the ore is taconite and wherein saidmineral comprises non-magnetic iron oxides.

18. The method of claim 17 wherein said conditioning step comprisesreacting the surfaces of iron oxide particles with a material selectedfrom the group consisting of fatty acids and sulfonic acids.

19. The method of claim 10 wherein said ore is contacted with magneticfluid in an amount within the range of 0.01 to 10 pounds of magneticfluid per ton of ore and wherein said magnetic separation isaccomplished by subjecting the magnetic fluid-treated ore to theinfluence of a magnetic field having a strength in excess of 1000 gauss.

20. A method for separating mixtures of particulate materials which donot respond to a magnetic field which comprises rendering the surfacesof at least one component of said mixture magnetic by selectivelywetting the surfaces of said component with a magnetic fluid, saidmagnetic fluid comprising an ultra-stable colloidal suspension ofmagnetic particles in a liquid carrier, said liquid carrier beingselected from the group consisting of hydrocarbons, fluorocarbons,silicone oils, water and esters, said magnetic fluid being capable ofreacting with an external magnetic fluid and displaying the behavior ofa homogenous Newtonian liquid, and thereafter subjecting the mixture toa magnetic separation whereby said magnetic fluid-wetted component isseparated from the remainder of the mixture.

21. The method of claim 20 wherein the mixture of particulate materialsis in liquid suspension and wherein a component of the mixture isselectively wetted by contacting the liquid suspension with a magneticfluid immiscible in said liquid.

22. The method of claim 21 wherein the mixture of particulate materialsis subjected to a conditioning step to modify the surface properties ofat least one constituent of the mixture prior to contacting the liquidsuspension with the magnetic fluid.

23. The method of claim 22 wherein the magnetic fluid is emulsified in aportion of said liquid prior to contacting said liquid suspension ofparticulate materials with said magnetic fluid.

24. The method of claim 23 wherein the liquid is water, wherein themagnetic fluid is hydrocarbon base and wherein the conditioning stepcomprises reacting the particle surfaces of at least one constituent ofthe mixture with a substance which renders said surfaces organophylic.

25. The method of claim 24 wherein the magnetic separation is performedin the liquid state whereby particles wetted with magnetic fluid arerecovered from the water suspension.

26. The method of claim 24 wherein the particulate suspension isde-watered and dried to a free-flowing state after being contacted withthe magnetic fluid and wherein the dried particulate mixture issubjected to a magnetic separation to recover a magnetically responsivefraction comprising particles wetted with magnetic fluid.

UNITED STATES PATENT AND TRADEMARK OFFICE EERTIFICATE 0F CORRECTIONPATENT NO. 2 3,926,789

DATE I December 16, 1975 INVENTOR(S) I Roland H. Shubert it is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Item [54] should read: MAGNETIC SEPARATION OF PARTICULATE MIXTURES Claim5, line 1 should read: .The method 6f claim 4-- En'gncd and Sealed thisfifteenth D8) of June 1976 [semi A nest.-

RUTH C. MASON C. MARSHALL DANN Arresting ()fl'irer (mnmissimmr ufParenrsand Trademarks

1. A METHOD OF RECOVERING A MAINERAL FROM THE GANGUE CONSTITUENTS OF ITSORE WHICH COMPRISES: COMMINUTING THE ORE TO A SIZE RANGE WHEREAT THEREIS ACHIEVED SUBSTANTIAL PHYSICAL LIBERATION OF THE MINERAL FROM THEGANGUE CONSTITUENTS OF THE ORE; RENDERING THE SURFACES OF THE MINERALPARTICLES MAGNETIC BY SELECTIVELY WETTING THE SURFACES OF SAID MINERALPARTICLES WITH A MAGNETIC FLUID, SAID MAGNETIC FLUID COMPRISING ANULTRA-STABLE COLLOIDAL SUSPENSION OF MAGNETIC PATICLES IN A LIQUIDCARRIER, SAID LIQUID CARRIER BEING SELECTED FROM THE GROUPS CONSISTINGOF HYDROCARBONS, FLUOROCARBONS, SILICONE OILS, WATER AND ESTERS, SAIDMAGNETIC FLUID BEING CAPABLE OF REATING WITH AN EXTERNAL MAGNETIC FIELDAND DISPLAYING THE BEHAVIOR OF A HOMOGENEOUS NEWTONIAN LIQUID, AND 2.The method of claim 1 wherein the surfaces of mineral particles are notreadily wet by water and wherein the surfaces of particulate gangueconstituents of the ore are readily wet by water.
 3. The method of claim2 wherein the magnetic fluid is immiscible with water and wherein themineral particles are selectively wetted with said fluid by contacting awater suspension of said comminuted ore with an amount of magnetic fluidsufficient to form a thin film on the surfaces of mineral particlescontained in the ore.
 4. The method of claim 3 wherein the mineral isselected from the group consisting of metal sulfides, metal oxides andcarbonaceous ores and wherein the magnetic fluid is hydrocarbon base. 5.The method of claim 5 wherein the comminuted ore is subjected to aconditioning steps comprising a chemical treatment which renders thesurfaces of mineral particles hydrophobic and organophyllic and whereinsaid magnetic separation is accomplished by subjecting the magneticfluid-treated ore to the influence of a magnetic field having a fieldstrength in excess of 1000 gauss.
 6. The method of claim 1 wherein thecomminuted ore is subjected to a conditioning step to modify the surfaceproperties of at least one constituent of the ore prior to wetting themineral particles with said magnetic fluid.
 7. The method of claim 6wherein said conditioning step comprises a chemical treatment whichrenders the surfaces of mineral particles hydrophobic and organophylic.8. The method of claim 7 wherein said conditioning step is carried outin an aqueous medium and wherein said magnetic fluid is immiscible withwater.
 9. The method of claim 8 wherein the mineral particles areselectively wetted with said magnetic fluid by contacting a watersuspension of comminuted and conditioned ore with an amount of magneticfluid sufficient to form a thin film on the surfaces of mineralparticles contained in the ore.
 10. The method of claim 9 wherein themagnetic fluid is hydrocarbon base and wherein the magnetic fluid is inthe form of a water emulsion when it is brought into contact with theore.
 11. The method of claim 10 wherein the magnetic separation is a wetseparation whereby mineral particles wetted with magnetic fluid arerecovered from the water suspension.
 12. The method of claim 10 whereinthe ore suspension is de-watered and dried to a free-flowing state afterbeing contacted with the magnetic fluid and wherein the dried ore issubjected to a magnetic separation to recover a mineral concentrate. 13.The method of claim 10 wherein the ore is a copper ore and wherein saidmineral comprises copper sulfide.
 14. The method of claim 13 whereinsaid conditioning step comprises reacting the surfaces of copper sulfideparticles with ferric ion.
 15. The method of claim 10 wherein the ore isa zinc ore and wherein said mineral comprises zinc sulfide.
 16. Themethod of claim 15 wherein said conditioning step comprises reacting thesurfaces of zinc sulfide particles with a dilute acid.
 17. The method ofclaim 10 wherein the ore is taconite and wherein said mineral comprisesnon-magnetic iron oxides.
 18. The method of claim 17 wherein saidconditioning step comprises reacting the surfaces of iron oxideparticles with a material selected from the group consisting of fattyacids and sulfonic acids.
 19. The method of claim 10 wherein said ore iscontacted with magnetic fluid in an amount within the range of 0.01 to10 pounds of magnetic fluid per ton of ore and wherein said magneticseparation is accomplished by subjecting the magnetic fluid-treated oreto the influence of a magnetic field having a strength in excess of 1000gauss.
 20. A method for separating mixtures of particulate materialswhich do not respond to a magnetic field which comprises rendering thesurfaces of at least one component of said mixture magnetic byselectively wetting the surfaces of said component with a magneticfluid, said magnetic fluid comprising an ultra-stable colloidalsuspension of magnetic particles in a liquid carrier, said liquidcarrier being selected from the group consisting of hydrocarbons,fluorocarbons, silicone oils, water and esters, said magnetic fluidbeing capable of reacting with an external magnetic fluid and displayingthe behavior of a homogenous Newtonian liquid, and thereafter subjectingthe mixture to a magnetic separation whereby said magnetic fluid-wettedcomponent is separated from the remainder of the mixture.
 21. The methodof claim 20 wherein the mixture of particulate materials is in liquidsuspension and wherein a component of the mixture is selectively wettedby contacting the liquid suspension with a magnetic fluid immiscible insaid liquid.
 22. The method of claim 21 wherein the mixture ofparticulate materials is subjected to a conditioning step to modify thesurface properties of at least one constituent of the mixture prior tocontacting the liquid suspension with the magnetic fluid.
 23. The methodof claim 22 wherein the magnetic fluid is emulsified in a portion ofsaid liquid prior to contacting said liquid suspension of particulatematerials with said magnetic fluid.
 24. The method of claim 23 whereinthe liquid is waTer, wherein the magnetic fluid is hydrocarbon base andwherein the conditioning step comprises reacting the particle surfacesof at least one constituent of the mixture with a substance whichrenders said surfaces organophylic.
 25. The method of claim 24 whereinthe magnetic separation is performed in the liquid state wherebyparticles wetted with magnetic fluid are recovered from the watersuspension.
 26. The method of claim 24 wherein the particulatesuspension is de-watered and dried to a free-flowing state after beingcontacted with the magnetic fluid and wherein the dried particulatemixture is subjected to a magnetic separation to recover a magneticallyresponsive fraction comprising particles wetted with magnetic fluid.